Deleting photos from Lightroom mobile

Without trying to confuse things too much, do you wish to have the photos currently in Lightroom on your phone synced to the Cloud? Or are these finished with and surplus to requirements?

If you want them in the Cloud, now you have purchased a plan, you'll need to let them sync. 

In this use case, you would want to not delete from Lightroom, and these full res files will be replaced with proxies locally once synced.

I seem to remember there may be an issue with existing photos when going from free to paid account, but cannot recall. 

Maybe Jim can?

It will not delete photos from your Camera Roll and it refers to Albums you have created in Lightroom, not in the native Photos app.

If you delete the photos, it will not delete the Presets BUT unless you have exported the photos you have edited in Lightroom, you will no longer have access to these edits.

Do you require the Photos and Edits in Lightroom to be backed up? Being as once they are deleted, they are gone (apart from exported photos and from any of the original photos in the Camera Roll). 

Photos taken with the in app Lightroom Camera would also be deleted if you have not exported them.

The Lightroom App and the Camera Roll do not sync, Lightroom only imports from it, if you have set it to.

I would make sure you have a back up of the Camera Roll photos, but assume you use iCloud.